Hydraulic tappet



c H, ALLEN HYDRAULIC TAPPET Filed oet. v. `1954v April 15, 19ss Zcyl- .L LIEFDI-D .LLEIA lvm @mi United States Patent HYDRAULIC TAPPET Clifford H. Allen, Cleveland, Ohio, assignor t o Thompson Products, Inc., a corporation of Ohio Application October 7, 1954, Serial No. 460,859 8 Claims. (Cl. 12S- 90) The present invention is directed to automatic clearance regulators or lash adjusters for providing a predetermined clearance in mechanical linkages, and finds par ticular applicability to the field of hydraulically operated automatic tappets of the type employed for opening and closing poppet valves in internal combustion engines.

Automatic clearance regulators, of which valve tappets are the best example, are designed to counteract looseness or play in a mechanical linkage system whether these irregularities are caused by mechanical difficulties or due to the effects of thermal expansion and contraction.

In the operation of these devices, it is important not only that the clearance regulator be operative to compensate for looseness in the system, but at the same time, it must not over-control the linkage to produce an undesirable tightness which, in the case of automatic tappets, would prevent full seating of the valve during operation.

There have been numerous types of automatic clearance regulators in use which function satisfactorily in an internal combustion engine when that engine has reached its operating temperature. However, in many instances, the operation of the automatic clearance regulators has been quite sluggish when the engine is first started. This sluggishness is frequently characteristic of valve tappets which employ -a slidable sealing means on the body of the tappet to prevent leakage of the hydraulic fluid from the tappet housing. Thus when such tappets stand idle for some time the sealing means may stick and a high break away force or an elevated temperature or both must be developed before the tappet can function.

Attempts to overcome this sluggish action by changing the stiffness of the return spring in the tappet assembly have not been successful because the use of such a stiffer spring has the undesirable effect of causing an undesirable tightness in the valve gear linkage after the initial collapse of the tappet return spring to its operating length.

With the foregoing in mind, an object of the present invention is to provide an improved automatic clearance regulator which operates effectively to provide a substantially constant clearance under widely varying conditions of operation.

Another object of the invention is to provide an improved automatic hydraulic tappet assembly for internal combustion engines in which the tappet assembly is capable of opening and closing the valve under widely varying temperature conditions.

Another object of the invention is to provide an improved hydraulic tappet assembly which can be manufactured in a much simpler manner, and with considerably less expense than automatic hydraulic tappets heretofore employed.

A still further object of this invention is to provide a tappet with a return spring having an extended low load length which will eliminate the necessity for heretofore required stops, having an operating length which will develop a good lash reclaiming load without impeding full seating of the engine valve, and having a collapsed length which will develop a load that is appreciably higher than the operating load so that the tappet will quickly assume an operating length.

A further description of the present invention will be lCC made in conjunction with the attached sheet of drawings in which:

Figure 1 is a view in elevation, with parts broken away and shown as cross section to illustrate the operation of the tappet mechanism in conjunction with the engine poppet valve;

Figure 2 is a longitudinal cross-sectional view illustrating the positions of the tappet parts just prior to the time that the engine poppet valve is open; and

Figure 3 is a view similar to Figure 2 but illustrating the position of the parts just after the engine poppet valve is closed.

As shown in the drawings:

Reference numeral 10 indicates generally the tappet assembly of the present invention, the movement of the tappet elements being controlled by means of a cam 11, supported on a rotatable carn shaft 12 of the internal combustion engine.

The vertical movement of the elements in the tappet assembly 10 is transmitted to a poppet valve 13 in the engine block by means of push rod 14 acting on the bottom of the valve stem. A spring retainer 1S is locked on the bottom end of the valve stem to bottom a valve spring 16 surrounding the valve stem and compressed between the retainer 15 and engine block.

As best seen in Figures 2 and 3, the tappet mechanism 10 includes a cylindrical barrel 17 having an open top and a closed bottom represented at 17a. A relatively light, cylindrical coiled spring 18 is disposed at the base of the hollow cylinder 17 and exerts a relatively light force on a choke ring 19 Which has a smaller outer diameter than the inner diameter of the barrel 17, as shown in the drawings. The choke ring 19 preferably has a generally triangular cross-section so as to provide a tapering valve seating face 19a along its upper surface.

Also included within the barrel 17 is an elastomeric syflthetic rubber cup seal member 21 which engages the walls of the barrel 17. The rubber cup member 21 has a central bore therethrough which receives the shank 22a of a valve member 22. The valve member 22 also has an enlarged head portion formed with a valve seat ing surface 22b which is arranged to become seated in the valve seating surface 19a of the choke ring 19.

The shank 22a of the valve member 22 is also slidably received within a lower plunger member 24 having an enlarged annular flange portion 24a bottomed against the upper surface of the rubber cup member 21.

An upper plunger member 26 is press fitted or otherwise secured to the top end of the shank 22. The upper plunger member 26 has a relieved portion 26a which receives an elastomeric sealing ring such as a synthetic rubber O ring 28 in sealing relation against the surfaces of the barrel 17 so as to prevent dirt and other contaminants from entering the interior of the tappet mechanism.

The upper plunger member 26 is also provided with a relieved shoulder portion 26b which serves to provide a means for containing a helical return spring 27 which normally separates the upper plunger member 26 from the lower plunger member 24. The spring 27 is heavier and stiffer than the spring 18. In the past, the selection of a spring 27 frequently resulted from a compromise of the various needs to be met. In some cases, the spring 27 was one which has as low a rate of change of return force with tappet length as possible. This type of spring, however, did not prove to be satisfactory particularly at low temperatures, as it resulted in sticking in the tappet mechanism particularly at the sealing ring 28. At the same time, the spring 27 should not have a high loading characteristic inasmuch as the higher operating force resulting thereby would in effect overcompensate for changes in clearance and thereby prevent full seating of the engine poppet valve.

In accordance with this invention the spring 27 is one which has a high return force when the tappet is collapsed but a nominaltappet operating force suicent to lengthen the tappet for eliminating lash in the valve train but insuflcient to impede full seating of the engine valve. As an example, the spring 27 may exert a load of about 20 to 22 pounds when the tappet is in its operating position, which is approximately 0.050 inch less than the extended length of the tappet. In the collapsed posi tion, where the spring 18 is fully collapsed, which is approximately 0.200 inch less than the extended length, the spring should exert approximately fty pounds or more force. As a general rule, I have found that the force exerted by the spring 27 when the tappet is collapsed due to leakdown after prolonged idleness should be at least about twice the force which the spring exerts when the tappet assumes its operating length. Further the spring should preferably quickly dissipate the operating force as it expands to an extended or full tappet length so that it will not force the elastometric sealing cup 21 onto the valve head 22b.

This extra high loading in the collapsed position can be obtained on conventional springs by reducing the number of active coils in the spring and by using a slightly larger wire diameter. This permits the spring to carry a greater maximum load without overstressing and also causes the load to increase more rapidly as the spring is collapsed or as the tappet is compressed.

The bottom portion of the tappet barrel 17, up to the upper cup member 21, is llled with a hydraulic fluid such as oil, a silicone polymer, or similar liquid having a reasonable amount of viscosity.

The choke ring 19 and the valve head 22b divide the lower portion of the tappet assembly into a lower pressure compartment A and a storage compartment B above the level of the valve and its valve seat. The return spring 27 bottoms the cup member 21 against the oil in the compartment B.

In the operation of the tappet mechanism, when the cam 11 is in a position for moving the tappet 10, the lold of the valve spring 16 is transmitted to the valve member 22 and through this valve member 22 to the choke ring 19. Since the choke ring 19 rests on the body of hydraulic tluid in the compartment A, the lifting pressure from the tappet barrel will be transmitted through the trapped oil in compartment A to the valve member 22 and finally to the engine valve 13. Some leakdown occurs between the outer periphery of the choke ring 19 and the inner wall of the barrel 17, thereby causing hydraulic lluid to ow from compartment A to the storage compartment B. As this leakdown occurs, the tappet valve 22 drops in the barrel, thereby shortening the assembly.

When the cam 11 has moved to a position in which it l no longer applies a valve opening load on the valve spring 16, the tappet return spring 27 takes over and expands to force the upper plunger 26 upwardly toward the open end of the barrel 17. As this occurs, the valve seating face 22b of the valve element 22 leaves its seated or nearly seated relation with the valve seating face 19a of the choke ring 19. As the valve element is opened, the compartment A is placed in full tluid communication with the storage compartment B. At the same time, the uid in the compartment B is under the compressive force exerted by the expanding return spring 27 through the lower plunger member 24 and the cup member 21, thereby forcing fluid from compartment B to compartment A. A condition of pressure equilibrium is promptly reached between the two compartments, and the valve seating face 22b will be seated, or very nearly seated, upon the valve seating face 19a of the choke ring 19.

It will be noted that the tappet assembly is somewhat selfcompensating for loss of hydraulic fluid since, if any uid should leak out of the storage compartment B,

the return spring 27 would be etective to move the lower plunger member 24 toward the bottom of the barrel 17, so that the rubber cup member 21 is always on top of a column of hydraulic iluid.

With a spring having the characteristics as described previously, the tappet will be partially shortened or collapsed in the usual manner over the normal operating range of the spring. However, due to the unique charact'eristics of the spring 27, as the tappet is collapsed beyond its operating range, due to leakdown caused by long idleness in an open engine valve condition with the force of the engine valve spring acting on the tappet, the return force provided by the spring 27 is much higher than would normally occur in a spring having the operating characteristics possessed by the spring prior to the collapse of the tappet. This substantial variation in the characteristics of the spring in the operating and in the collapsed position of the tappet has been found to substantially eliminate the sluggish operation of the tappets previously noted, particularly during cold operation of the engine while at the same time eliminating the danger of over-compensating.

Thus, if clearance should occur in the valve u'ain, the return spring 27 acts on the lower plunger member 24 and the upper plunger member 26 moving them axially of the tappet barrel 17. As this occurs, hydraulic fluid is forced from the chamber B to the chamber A, thereby raising the valve member 22 and causing an elongation of the assembly and a reclaiming of any gap imposed by looseness or slack in the linkage. Flow from the storage compartment B to the pressure compartment A occurs very rapidly through the open choke ring 19 while reverse ow is impeded due to the fact that the valve member 22 is, at that time, seated in the choke ring 19 and only a small area is available through which the hydraulic uid may how.

The provision of the unique type of return spring 27 in the tappet, also has additional advantages in addition to the operational advantages mentioned above. For one, it makes the design of the tappet valve member 22 considerably easier, since it eliminates the heretofore required stops to keep the rubber cup 21 away from the valve head 22b and thus permits the use of a stem on the valve member 22 of substantially uniform diameter. In

previously known tappets of the herein disclosed type, the

valve stem had to be provided with a shoulder which engaged a spun over portion of the lower plunger member 24, the purpose being to limit the axial movement of the lower shoulder member 24 -along the valve member 22. Otherwise, the rubber cup ring 21 might be forced over the enlarged end of the valve member 22b during assembly. The reduced diameter stem portion could not function as a lbearing or guide wall in the plunger and smooth sliding ts of the plungers on the stems were difcult to obtain. f

In the present form of tappet assembly, however, this stop precaution is not essential because the return spring 27 exerts only a relatively small amount of force insucient to force the rubber cup member 21 over the head end 22b of the valve member 22 by virtue of the normally small compression which exists in that spring. In other words, itis only when the spring 27 is compressed to its operating length that the compressive force of the spring comes into play. The elimination of the reduced diameter valve stern to form the stop shoulder makes possible full use of the stem as a guide in the bearing provided by the lower plunger. The improved piloting of the tappet valve member through the lower plunger member due to the increased bearing length eliminates sticking or cocking of the valve.

It will 'be evident that various modilcations can be made to the described embodiment without departing from the scope of the present invention.

I claim as my invention:

l. A clearance regulator which comprises a barrel hav ing a closed bottom and an open top, a first spring bottomed on said closed bottom, a choke ring seated on said first spring, a valve element having a valve head arranged to be received in seated relationship within said choke ring, a cup sealing member slidably mounted on said valve element adjacent the valve head and arranged to confine uid within the lower portion of said barrel, a first plunger slidable in said barrel, bottomed on said sealing member and slidably guiding said valve element, a second plunger affixed on said valve element, a second spring between said first and second plungers effective to elongate the regulator, and a resilient sealing member between said second plunger and the inner wall of said barrel, said second spring having a free expanded length insufficient to force the cup sealing member tightly against the valve head, having a partially collapsed operating length developing an appreciable force to elongate the tappet, and having a fully collapsed length developing a tappet elongating force substantially greater than said appreciable force.

2. A clearance regulator which comprises a barrel having a closed bottom and an open top, =a first spring bottomed on said closed bottom, a choke ring seated on said first spring, a valve element having a valve head arranged to be received in seated relationship within said choke ring, ia cup sealing member slidably mounted on said valve element adjacent the valve head and arranged to confine fluid within the lower portion of said barrel, a first plunger slidable in said barrel, bottomed on said se -l -g member and slidably guiding said valve element, a second plunger affixed on said valve element, a second spring between said rst and second plungers effective to elongate the regulator, and a resilient sealing member between said second plunger and the inner wall of said barrel, said second spring having a free expanded length insufcient to force the cup sealing member tightly against the valve head, having a partially collapsed operating length developing an appreciable force to elongate the tappet, and having a fully collapsed length developing a tappet elongating force at least twice the amount of said appreciable force.

3. A thrust valve type hydraulic tappet comprising a barrel having `a closed bottom and an open top, a first spring bottomed on said closed bottom, a choke ring movable in response to movement of said first spring, a valve element slidable in said barrel and having a valve seating face arranged to be seated in said choke ring, a cup sealing member slidably mounted on said valve element, a body of hydraulic fluid in said barrel between said cup sealing member and said closed bottom, a first plunger slidable in said barrel and vbottomed on said sealing member, a second plunger slidable in said barrel, a second spring separating said first and second plungers to elongate the tappet, and a resilient sealing member between said second plunger and the inner wall of said barrel, said second spring having a characteristic such that the tappet elongating force developed thereby during operation of the tappet is less than half the force developed when the tappet is fully collapsed.

4. A thrust valve type hydraulic tappet comprising a cylindrical barrel having a closed bottom and an open top, a first spring bottomed on said closed bottom, a choke ring movable in response to movement of said first spring, a valve element slidable in said barrel, said' valve element including an enlarged head portion arranged to be seated in said choke ring, said valve element having a substantially uniform diameter throughout its length, except for said enlarged head portion, a cup sealing member slidably mounted on said valve element, a first plunger slidable in said barrel and bottomed on said sealing member, a second plunger spaced from said first plunger, a second spring separating said first plunger and said second plunger to elongate the tappet, and a resilient sealing member between said second plunger and the inner wall of said barrel, said second spring having a characteristic developing a substantial tappet elongating force when slightly collapsed from a free condition and then quickly developing a tappet elongating force at least two times said substantial force when the ta-ppet approaches a fully collapsed condition.

5. A thrust valveV type hydraulic tappet comprising a cylindrical barrel having a closed bottom and an open top, a first spring bottomed on said closed bottom, a choke ring movable in response to movement of said first spring, a valve element slidable in said barrel and having a valve seating face arranged to be seated on said choke ring, said valve element having a substantially uniform diameter throughout its length except for s'aid enlarged head portion, a cup sealing member slidably mounted on said valve element, a first plunger slidable along said valve element and bottomed on said sealing member, said first plunger having an axial bore of uniform diameter receiving said valve member in sliding relation, a second plunger spaced from said first plunger, a second spring separating said first plunger and said second plunger to elongate the tappet, and a resilient sealing member between said second plunger and the inner wall of said barrel, said second spring having a characteristic such that the force exerted by said second spring at one end of travel of said'valve member while said sec ond spring is substantially compressed is at least two times the force exerted by said second spring between said first plunger and said second plunger when the tappet length is in its operating range.

6. A tappet assembly which comprises, a barrel providing a trapped fluid chamber, a plunger slidable in said barrel adapted to be bottomed on fluid in the charnber, a valve having a stem slidably guided in said plunger, and a head adapted to be submerged in fluid in the charnber, a choke ring freely slidable in the fluid chamber coacting with said head, a first spring urging the choke ring against the head, a second spring acting on the plunger and valve to elongate the tappet, said second spring being substantially stiffer than the first spring, havinga free length insufficient to place the plunger and valve head in thrusting relation, developing an appreciable tappet elongating force when slightly collapsed from said free length, and developing at least twice said appreciable force when said first spring is fully collapsed.

7. In a hydraulic engine valve tappet or the like clearance regulator, a housing, a valve slidably mounted in said housing, and a valve seat in said housing coacting with the valve, the improvement of a coiled return spring acting on saidvalve to elongate the tappet and said spring having the number of coils and the diameter of the coiled material correlated to develop a tappet elongating force when the tappetlis collapsed which is at least twice the force developed when the tappet is at an operating length.

8. In a hydraulic clearance regulator, a housing valve means having a uniform diameter shank slidable in the housing to vary the effective length of the regulator, a return spring acting between the housing and said valve means, and a resilient ring slidably mounted along said shank, said return spring having a free expanded length insufficient to force said resilient ring ofi said shank, having a partially collapsed operating length developing an appreciable force to elongate the regulator, and having a fully collapsed length developing an elongating force substantially greater than said appreciable force.

References Cited in the file of this patent UNITED STATES PATENTS Re. 21,931 Voorhies et al Oct. 21, 1941 2,213,195 Banker Sept. 3, 1940 2,570,854 Pierce Oct. 9, 1951 2,682,865 Voorhies July 6, 1954 2,742,030 Gleeson Apr. 17, 1956 2,742,031 Touschek Apr. 17, 1956 

